Fixed-bed (or packed-bed) bioreacto

Fixed-bed (or packed-bed) bioreactors are frequently utilized for immobilized plant cell, differentiated plant tissue or organ systems. For the application of cell cultures, cells are immobilized in appropriate microcarriers (Gilleta et al., 2000 and Medina-Bolivar and Cramer, 2004), which are packed in the fixed zones, resulting in high solid–liquid specific interfacial contact areas. A medium reservoir is used to circulate the oxygenated nutrient medium through the bed and the spent medium containing the product that returns to the reservoir can be harvested in batch or continuous mode. The major disadvantages of the fixed-bed bioreactors are their relatively poor mass and heat transfer capability due to low liquid velocities. Fixed-bed bioreactors have shown applications in perfusion animal cell cultures (Meuwly et al., 2007), where cells are immobilized within microcarriers and therefore they are less sensitive to shear force than in suspension culture. Although the microenvironment created for the immobilized cells within the carrier matrix are different from that in the bulk liquid, with the appropriate selection of carriers for cell immobilization, high cell density and high productivity can be achieved.